This invention concerns improvements in or relating to ophthalmic lenses, including in particular contact lenses and spectacle lenses.
The human eye is known to exhibit longitudinal chromatic aberration so that objects at the same distance but of different colours cannot all be sharply focussed at the same time. Thus, to effect simultaneous sharp focussing orange and red objects need to be placed farther away than a green object while blue and violet objects have to be nearer the eye than the green object. The extent of the effect is about one dioptre and there is evidence to suggest that the eye/brain system makes use of this to avoid refocussing, concentrating on the blue components of objects that are close and on the red components for distant vision.